|State (class)|Vacator|Reason for change|Successor|Date of successor's formal installation|
|---|---|---|---|---|
|New Hampshire (3)|Vacant|Disputed election. Norris Cotton appointed to seat until special election resolved dispute.|Norris Cotton (R)|August 8, 1975|
|New Hampshire (3)|Norris Cotton (R)|Successor elected September 18, 1975|John A. Durkin (D)|September 18, 1975|
|Michigan (1)|Philip Hart (D)|Died December 26, 1976|Donald W. Riegle, Jr. (D)|December 27, 1976|
|Missouri (1)|Stuart Symington (D)|Resigned December 27, 1976|John Danforth (R)|December 27, 1976|
|Nebraska (1)|Roman Hruska (R)|Resigned December 27, 1976|Edward Zorinsky (D)|December 28, 1976|
|Ohio (1)|Robert Taft, Jr. (R)|Resigned December 28, 1976|Vacant|Not filled this term|
|Rhode Island (1)|John O. Pastore (D)|Resigned December 28, 1976|John Chafee (R)|December 29, 1976|
|Minnesota (2)|Walter Mondale (DFL)|Resigned December 30, 1976 after being elected Vice-President of the United States.|Wendell Anderson (DFL)|December 30, 1976|
|California (1)|John V. Tunney (D)|Resigned January 1, 1977|S. I. Hayakawa (R)|January 2, 1977|

Question: how many total replacements happened in this session?
Answer: 9